A gifted cinematic presence since her Oscar-nominated "Atonement" debut at age 12, Saoirse Ronan has played everything from a young assassin raised among wolves in "Hanna" to a resident of "Grand Budapest Hotel's" imaginary Zubrowka.

But "Brooklyn," her new film debuting Monday in the Premiers section at Sundance, was something different.

"Playing someone normal was the biggest challenge," the now 20-year-old actress says. "I wasn't used to it."

Ronan in person is warm, lively and aware, the kind of can-do individual who will jump up to get a waitress herself if service in a restaurant isn't what it should be.

Ask her how old she was when she began acting and she'll reply, with amusement and style, "I was in the womb, Kenny. I was zero. It started when my mum and dad had a glimmer in their eye."

So it's no surprise that not playing ordinary people was not a plan on Ronan's part, more that "an awful lot of scripts written about normal girls just weren't very interesting. They're about makeovers, about wanting to be the popular girl or getting the boy. I didn't find anything interesting enough for years, and then Eilis came along."

Eilis is "Brooklyn's" protagonist, a young woman who emigrates from Ireland to that celebrated New York borough in 1952 and ends up contending with homesickness, culture shock and a variety of romantic involvements.

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Impeccably directed by John Crowley and elegantly adapted by Nick Hornby from a novel by Colm Tóibín, "Brooklyn" is classic filmmaking beautifully done, illustrating the power of restraint in dealing with emotional material. And as Ronan's first time "telling an Irish story in an Irish film," it has special meaning.

"I get very emotional when I talk about it; I hope I'm not going to start crying," the actress says. "I never had a film affect me like that. It was very much a passion project for all the people involved."

It's not only that "for generation after generation, the relationship has been so close between Ireland and the United States" but there's a personal connection as well.

Bobby Bank / GC Images / Getty Images

Actors Saoirse Ronan and Emory Cohen on the set of "Brooklyn" on May 21, 2014 in New York City.

Actors Saoirse Ronan and Emory Cohen on the set of "Brooklyn" on May 21, 2014 in New York City. (Bobby Bank / GC Images / Getty Images)

"My mom and dad made that journey," says Ronan, who was born in the New York area and moved back to Ireland with her parents when she was 3. "The town we shot in in Ireland was close to where I grew up, where I spent my childhood. Every second scene knocked me over by how it affected me."

So for the actress, another of the challenges of "Brooklyn" was "trying to find a balance, giving the story color, but at the same time holding back, keeping control. It was hard. I was very aware I didn't want to do too many crying scenes, I didn't want to do too much blubbering. That gets very boring, unless you really need it."

Helping her greatly with her performance was Crowley, a director with extensive experience in theater whose films include "Boy A" and "Closed Circuit."

"John is a theater director at heart, it's all about community, about communicating with your actors," Ronan says. "He was involved in everything, but when it came to the acting, he was so tied into every single thing you were doing, performance was absolutely everything to him.

"He gave you notes after a take, he constantly moved you around. In the time it took to do eight takes, you discovered more and more about what you were doing. He revealed to me so many different elements in my character I hadn't really considered before. He made me more present because of the way he works."

Because Ronan is roughly the same age as Eilis, and in fact has just gotten a place of her own in London, elements of Eilis' situation ring especially true.

"Really, this film is about choice, about when you've gone through enough life experience to make a choice for yourself," Ronan says. "Eilis is finally at the stage in her life where she knows not what she needs to do but what she wants. That's a really empowering thing."

Part of the choice Eilis has to make involves two suitors, played by Domhnall Gleeson and Emory Cohen. The men do not meet in the film, but the cast did have an introductory dinner together, and Ronan jokes that "once we got past the fact that the film wasn't real, they were able to chill out and have fun."

Fun was a theme of Ronan's early years in New York, where her father was a working actor. "My parents were both very expressive people, and exposure to American humor broadened their world," she says.

"Their friends had big personalities, and the way they interacted with me was not the typical way grown-ups would be with kids. They talked to me like an equal, they encouraged me to perform, to be myself."